It is known to perform the targeted analysis of analyte components using either single or tandem quadrupole mass filters. During single ion recording (SIR) analysis, the mass filter(s) is set to only transmit ions having a mass to charge ratio value that corresponds to that of the known target ion. These transmitted ions are then detected. In multiple reaction monitoring (MRM), a first quadrupole mass filter Q1 is provided that is set to only transmit parent ions having a mass to charge ratio value that corresponds to that of the known target ion. The transmitted parent ions are then fragmented and the resulting fragment ions are transmitted through a second quadrupole mass filter Q2. The second quadrupole mass filter Q2 is set to only transmit fragment ions having a mass to charge ratio value that corresponds to that of a desired product ion. These transmitted fragment ions are then detected.
The analyte ions may be separated by chromatography prior to being analysed by the mass filters. Prior to analysis, it is known to determine the chromatographic elution or retention time for each target analyte using pure standards or standards prepared in a representative matrix. Once the retention time window in which each target analyte elutes is determined, the mass filter or filters are programmed to transmit these values at the appropriate time after the start of the chromatographic separation. Standards of different concentrations are used to produce quantification calibration curves relating the signal intensity detected to the amount of analyte introduced.
In normal operation the ion current at the detector is integrated for a period of time (i.e. the dwell time) for each mass filter setting. At each time period a single time-intensity (TI) point is recorded. For a given target species, a plot or chromatogram is produced of ion current detected as a function of chromatographic retention time. Chromatographic peaks within the retention time window for the target analyte may be integrated to perform quantification of the target analyte.
It is desired to provide an improved method of mass spectrometry and an improved mass spectrometer.